1. Field of the Invention
The present invention relates generally to the field of brushless DC motor drives. More particularly, the invention relates to a drive for a brushless DC motor which is integrated or packaged with the motor in an end cap forming a unitary drive and motor assembly.
2. Description of the Related Art
A wide range of electric motors have been developed and are presently in use for driving a vast array of devices in rotation. In general, such motors fall within a number of classes, such as alternating current motors (e.g. induction motors) and direct current motors. In one type of direct current motor, commonly referred to as a brushless or synchronous motor, a rotor is supported in rotation in a housing and is surrounded by a stator or armature. The rotor may include a series of permanent magnets, the field of which cooperates with fields generated by stator windings to drive the rotor in rotation. Pulsed or alternating electric current is fed to the stator coils and the rotor is thus driven at a speed which is a function of the pulse frequency of the drive energy or a function of the duty cycle of the pulsed energy.
Because the rotational velocity of brushless DC motors may be easily controlled by controlling the pulse frequency or pulse width duty cycle of the incoming power, it is generally known to regulate speed of such motors by means of controllers configured to convert incoming power to a desired controlled frequency or duty cycle. The controlled power is then transmitted to the motor and the rotor is driven at a speed which is a function of the frequency or duty cycle. In one particularly useful technique for controlling brushless DC motors the rotational velocity of the motor is detected by sensors within the motor assembly, and the driving frequency or duty cycle is regulated in a closed-loop manner to maintain this rotational velocity at a desired level based upon the feedback information supplied by the sensors and upon a velocity control or command signal. The velocity control signal may be supplied in a variety of manners, such as via an operator-adjustable potentiometer or other input device, or by an automatic controller.
Controllers, also referred to as drives for brushless DC motors may convert either incoming alternating current electrical energy or direct current energy into the controlled-frequency or controlled-duty cycle energy required for driving the motor. In the former case, sometimes referred to as "off-line" drives, a full-wave rectifier circuit is typically included in the drive. Such drives are well suited to applications in which an alternating current power source is readily available, such as in most residential and industrial applications. However, in a number of applications, such alternating current power sources are unavailable and the drive circuitry must convert direct current energy from a source, such as a battery or generator, to the controlled-frequency or pulse width duty cycle energy required to drive the motor. Such applications include machinery mounted on or coupled to vehicles such as automobiles, buses, boats and so forth.
Conventionally, brushless DC motor drives, particularly of the type suited for receiving direct current electrical energy, have been designed and assembled separately from the motors with which they are associated. For example, the drive may be mounted within a separate enclosure supported on the DC motor housing. Conductors then extend from the drive enclosure through the motor housing to transmit the pulsed electrical energy to the motor stator. Alternatively, the drive may be formed as a modular unit which is added to an end of the motor housing.
While both of these known arrangements enable the motor to be assembled completely separately from the drive, the resulting package is somewhat unwieldy and may be difficult to install in certain applications. For example, in applications such as small fan drives, it is usually advantageous to maintain the motor and drive package as small as possible. In addition, in all applications the overall cost of the motor and drive package is often minimized when the number of separate parts in the package is reduced. However, conventional drives manufacturers have yet to develop brushless DC motor drives which satisfy the need for small, integrated units which are both economically priced and of high performance.
There is a need, therefore, for an improved motor drive which can be integrated with a brushless DC motor to form a single, compact and economical package. In particular, there is a need for a drive configured for coupling to a source of energy for a variety of applications, such as in vehicles. The drive should, ideally, afford the user the advantages of being easy to install, and provide a wide range of controllable parameters such as speed and torque.